Satellite terminals slim down for battlefield missions

The drive to provide more connectivity to troops on the move is leading to solid growth for very-small-aperture terminals (VSATs). Compact VSATs are bringing many benefits to mobile warfighters, offering reduced weight, longer battery lifetimes and higher bandwidth.

The advances come in many areas, lighter materials, better batteries and continuing advances in electronics. One of the big enablers is the shift to the Ka band, led by the military’s Wideband Global Satcom (WGS) program. This band of spectrum offers more throughput, but for mobile forces, its biggest advantage might be the ability to use smaller antennas.

“We’ve got man-portable terminals that use a 24-inch parabolic antenna,” said Tony Janetta, chief technology officer at L-3 Global Communications Solutions. “With the WGS satellites, warfighters get the same throughput as they did with 2- to 4-meter antennas. Antenna size has gone from 8 feet to 2 feet, largely due to higher capabilities on the satellite.”

The Ka band lets warfighters carry smaller systems into the field and access more bandwidth. The technology has greater throughput than many alternative technologies.

It’s not only Ka-band technology that’s enabling the shift to VSATs. Next year, Inmarsat will launch a satellite that has extensive L-band communications and capabilities that will provide more narrow beam connections.

“Alphasat I-XL will add 400 narrow beams," said John Munoz-Atkinson, director of land business development at Inmarsat Government Services. "That means the aperture can be smaller so warfighters can carry smaller antennas.” L-band links can penetrate bad weather better than the Ka band can, he added.

Technical advances

As new satellite technology is making it easier to send more information to special operations forces and other mobile squads, there are big changes in the technology that troops carry on missions.

Engineers turning to lighter materials, modern batteries and state-of-the-art electronics to lighten the load that warfighters carry. Even though VSAT antennas are smaller than their predecessors, engineers are making these compact units as light as possible without sacrificing durability.

“Some of the trends are the use of smaller, carbon fiber reflectors, which are rugged and lightweight, and no-tools-required assembly of antenna systems, reflectors, feed assembly and tripod mount,” said Richard Hadsall, CTO at MTN Satellite Communications. “Systems need to be completely preintegrated to relieve the need for human intervention.”

Improving battery life is also at the forefront of terminal design. “Extended battery life is accomplished by using lithium ion batteries. Additionally, the use of smart batteries that provide real-time information to the user provides for better insight to the battery status and life,” West said.

Electronic engineers are also using a range of techniques to further cut power consumption. One of the most effective methods is to use sleep modes for devices that don’t need to be active all the time. These advances often mirror the trends set by the cell phone industry.

Many communications providers have migrated to Time Division Multiple Access technology, which lets several users share a frequency. The concept, also used in some cell phones to increase the number of users, can also help trim battery consumption. That’s because remotes in the field only transmit during a fraction of the available time.

“Normally, when the modem is on, the block upconverter is on all the time, constantly drawing power,” said Karl Fuchs, vice president of technology at iDirect Government Technologies. “We have a separate channel for the BUC, powering it down when it’s not needed. The battery savings can be 30 percent to 45 percent.”

With those techniques, the benefits can often ripple to make substantial changes in overall system size and lifetimes. “If we can get our power amplifier operations down by 25 percent, we could see huge benefits in size, with smaller heat sinks," Janetta said. "Using less power also means longer battery lifetimes.”

Another way to trim power consumption is to send more data in a given time frame so systems can stay in sleep modes for longer periods. Engineers are working to devise ways to squeeze more signals into the same amount of satellite bandwidth. They are also working on techniques that minimize the effects of rain and fog.

“There are advances in waveform efficiency that let us get more bits per hertz,” Fuchs said. “The spectral efficiency of satellite systems is paramount. Things like adaptive inbound channels that rapidly adapt to atmospheric changes are extremely important.”

The simpler, the better

As with PCs, design teams are now focusing heavily on plug and play and ease of use.

When mobile forces set up VSATs, they don’t want to spend a lot of time tightening bolts and adjusting the antenna to find its optimal position. Most of the steps are handled automatically, saving time and providing the best performance possible.

“With most terminals today, if they’re configured properly, you push a button and the system will target the antenna,” Janetta said. “The shift to Ethernet ports and IP communications makes it easy to plug everything in, setup is virtually non-existent. We’ve got a human/machine interface that lets users look at icons to set things up and troubleshoot if need be.”

There’s also a push to ensure that the data sent to warfighters is useful. That is becoming more critical because the volume of data that can be sent deep into the field is as voluminous as that transmitted to command centers.

Small warfighter teams in the midst of maneuvers often won’t have much time or manpower to study video streams. Product developers are looking at techniques to revise images so they can be understood on screens used in conjunction with smaller VSAT systems. They’re also attempting to devise techniques that simplify data streams and highlight critical points.

“In a tactical environment, staring at video can be a detriment as much as a help,” said David Martin, vice president of tactical satcom business development at Windmill International. “Now that the ability to get the pipe to warfighters has been solved, a lot of work is needed to provide the right supporting information to the end-users through that pipe in a way that they can use it quickly and effectively.”

The continuous shrinkage in the size of technology might lead some warfighters to envision a day when their satellite systems are as small as their cell phones. Although there will be improvements, system providers note that satellite signals will always need a fairly large antenna and sophisticated electronics that take more space than cell phone systems.

“There are theoretical limits," Janetta said. "There are still 23,000 miles between us and the satellite.”